Human faces are very powerful. User Experience designer Aarron Walter describes in his book Designing for Emotion why we appreciate human faces so much. He explains that we are constantly exploring the world around us by looking for something familiar. Familiarity gives us a feeling of comfort and reassurance.
When we see a face, we are automatically triggered to feel something or to empathize with that person. If we recognize content on a website — such as a problem, dilemma, habit or whatever else — we feel connected and understood.